Compressing CO2.

Main Question or Discussion Point

Hi,

I am doing a design project designing a LCO2 laundering system to operate on the moon. I was looking to get some insight into how you compress CO2. Can a standard air compressor with a storage vessel that can contain sufficient pressure work to compress CO2?

Correct, that is part of the design. We allow the CO2 to move in the system as a gas, then compress it enough to have a half full, horizontal axis washing machine.

The system is being designed for the moon so the equivalent system mass (ESM) has to be as low as possible. Meaning that the energy use, overall mass, volume, weight, crew member time, etc have to be minimized. So by design the CO2 would be moved by a pressure differential.

The only problem that i am having is that I don't believe a standard air compressor will work. I need to reach right around 1000 psi. I know that there are scuba diving compressors that easily can compress air to 5000 psi, but I am not sure whether or not I can use the same compressor for CO2.

I design recip compression equipment that works in the range between liquid and gas. The fluid properties can vary significantly depending on whether or not the fluid is liquid, gas or supercritical, the main properties you will be concerned with are compressibility which goes into determining the volumetric displacement of each stage of compression. To design such a machine you need to have a good computerized fluids properties database that you can link to a program for determining flows and pressures. NIST has a program I would recommend called REFPROP. You can purchase it online here: http://www.nist.gov/srd/nist23.cfm

Once you're familiar with how to use it, you'll want to create programs that calculate flow rates and pressures, power usage, valve pressure drops and valve dynamics, etc... That way you can change cylinder diameters, strokes, RPM, compression ratio, interstage cooler capacity, etc.... which will give you a rough idea of what you need to do to make the machine feasible. It won't however, give you any information about materials, seal design, valve design, etc... that is critical to making a machine reliable and able to perform as well as those theromodynamic models indicate.

A better way to get the design created and a pump manufactured is to create an engineering specification for what you need and send it out for quote to a handful of manufacturers that specialize in that kind of equipment. You can do the feasibility study on your own, determining what pressures and flows you want and how large the machine might be. But once you get into the details, you'll need to find an engineering team with some experience designing the pump/compressor.